Load in surveying instruments, surveillance cameras, and semiconductor manufacturing and testing devices require high-precision in their positioning control. Wide spread use of battery driven products has lead to growing demand in both efficient operation and high-precision positioning.
JP 2005-292898 A discloses a positioning control unit that generates command values to be delivered to a servo motor by combining a target position with corrected data generated in advance for absolute positioning control. The corrected data is generated by positioning the servo motor at predetermined constant angles, measuring the specified absolute positioning by a high-resolution encoder, and obtaining angle error data from the encoder position data of the servo motor and the high-resolution encoder position data.
JP 2007-181353 A discloses a surveillance camera driver capable of high-responsive operation employing a step motor and a surveillance camera system. The surveillance camera driver provides feedback on rotational position of the rotor and switches energization of the coil so that voltage induced by the permanent magnet of the step motor and the coil current are placed in a predetermined phase relation. Thus, step-out is less prone to occur and the surveillance camera driver can be driven with high efficiency and high responsiveness. Also, since the surveillance camera driver is provided with a position control loop, coil current flows only when displacement occurs from the target position and no coil current flows when no displacement occurs from the target position. Such arrangement results in less current consumption, thereby providing increased battery drive time.
High precision positioning often involves a drive system employing gears as disclosed in JP 2007-181353 A. Gears are used since provision of a predetermined gear ratio allows positioning precision of the motor itself to be relaxed. However, increasing demand for high efficiency operation requires direct load drive without gears. Since direct load drive often results in lack of motor output torque on the load, it becomes even more difficult to perform high precision positioning against load inertia.